Photoflash lamp

ABSTRACT

A photoflash lamp in which the filamentary combustible within the lamp envelope comprises a plurality of fine strands of foil each having a uniformly coiled or crimped configuration for increasing the number and reducing the size of molten droplets produced when the foil is burning. The coiled or crimped configuration also tends to prevent roping of the strands. If coiled, the strand configuration may have a diameter of from 0.010 to 0.030 inch and a pitch of from 20 to 300 turns per inch, and if crimped, the length of each straight segment of strand may be from 0.010 to 0.060 inch and the angle of each bend in the strand may be from 60* to 165*.

United States. Patent 1 Bouchard et a].

[ Feb. 19, 1974 3,630,650 12/1971 Stadtbergen et a1 431/95 Primary ExaminerCarroll B. Dority, Jr. Attorney, Agent, or Firm-Edward .1. Coleman [57] ABSTRACT A photoflash lamp in which the filamentary combustible within the lamp envelope comprises a plurality of fine strands of foil each having a uniformly coiled or crimped configuration for increasing the number and reducing the size of molten droplets produced when the foil is burning. The coiled or crimped configuration also tends to prevent roping of the strands. If coiled, the strand configuration may have a diameter of from 0.010 to 0.030 inch and a pitch of from 20 to 300 turns per inch, and if crimped, the length of each straight segment of strand may be from 0.010 to 0.060 inch and the angle of each bend in the strand may be from 60 to 165.

20 Claims, 7 Drawing Figures PATENTEDFEBIQIQM "3.792.951

' saw 2 [If 2 G E COILED SHRED Z L5 cm LONG Lu 2 o- 3 STRAIGHT SHRED 6: L5 cm LONG TIME IN MSEC.

FIG.6

PHOTOFLASH LAMP BACKGROUND OF THE INVENTION This invention relates to photoflash lamps and particularly to flashlamps containing a filamentary combustible.

The combustible material commonly employed in presently available photoflash lamps consists of a quantity of filamentary material of a type commercially known as shredded foil. The material is made by cutting or shredding a thin sheet or ribbon of suitable metal foil into thin strands. Aluminum and magnesium foil have been used for this purpose, although more recently, zirconium and hafnium have been found to provide significant photometric advantages.

In relatively large size flashlamps, it has been customary to employ shredded foil strands having a length-of the order of 8 inches. The use of such long strands in subminiature lamps (a volume of less than 1 cc.), however, increases the difficulty of obtaining good distribution of the shredded foil by the pneumatic foil-loading methods which are conventionally used. Poor distribution of the shredded foil in the lamp envelope adversely affects the timing of the lighting flash and also decreases the efficiency of burning the combustible material, thereby resulting in reduced lighting output from the lamp.

To improve the distribution and ignition characteristics of the shredded combustible in smaller size lamps, a variety of strand configurations have been employed. According to one common method of manufacturing subminiature flashlamps, combustible foil strands of about 4 inches in length are blown into the lamp envelope to result in a mass of relatively large intermingled loops. The large strand loops tend to lie along the internal wall of the lamp envelope in a helical configuration, resulting in many areas of lateral contact between the combustible strand and the wall of the glass envelope. The large mass of the envelope wall tends to greatly quench any emitted light from molten droplets in these lateral contact regions, this quenching effect being particularly pronounced in flashlamps with small internal volumes. Further, upon ignition, the large loop configuration tends to produce relatively large molten droplets. Large droplets have distinct disadvantages over smaller droplets. For example, the large droplets tend to radiate light well beyond the useful range (typically 30 msec.) desired in flashlamps. In addition, large droplets can cause more pronounced glass cracks when impinging upon the lamp wall during the combustion process.

To overcome the aforementioned disadvantages of long strands in subminiature flashlamp, a copending US. Pat. application Ser. No. 179,056, filed Sept. 9, 1971 in the names of David R. Broadt and Donald E. Armstrong and assigned to the assignee of the present application, describes the use of short shreds (e.g., strand lengths of 0.200 inch) arranged in a manner to keep the bulk of the combustible material away from the wall of the lamp envelope. Accordingly, the use of shorter strand lengths significantly increases the efficiency of combustion in lamps of less than 1 cc. internal volume by substantially reducing the lateral contact areas between the combustible material and lamp wall. In addition the shorter shreds produce smaller molten droplets during the combustion process. In the case of flashlamps having an internal envelope volume substantially larger than 1 cc., however, the short shred configuration would appear to be somewhat impractical since support of the desired shred distribution by the envelope wall would be virtually impossible with standard loadings.

A third configuration directed towards optimizing combustion in subminiature lamps by supporting the shredded foil away from the envelope wall is described in US. Pat. No. 3,630,650. According to this arrangement, shreds of mm. (about 4 inches) in length are crumpled to have a random configuration of from 8 to 50 sharp bends per strand to effect point contact between the filling and envelope wall. When distributed in the lamp, each 100 mm. shred forms a ball with a cross-sectional area of from 40 to 8 mm.*. Although providing significantly improved light output over, that obtainable using the intermingled loop configuration, this crumpled foil packing geometry does not permit the degree and uniformity of droplet size control attained by the present invention. Further, the use of crumpled and balled shreds is not advantageous in terms of producing small molten droplets during combustion since the proximity of droplets in the wadded configuration can cause coalescence of individual droplets, which in turn can cause an increase in bulb cracks.

SUMMARY OF THE INVENTION In view of the foregoing, a principal object of this invention is to provide a photoflash lamp having improved light output characteristics.

A particular object of the invention is to provide a self-supporting filamentary combustible for a flashlamp which produces an increased number of molten droplets of significantly reduced size when burning.

These and other objects, advantages and features are attained, in accordance with the invention, by providing a filamentary combustible in which the configuration of each of the strands comprises substantially uniform periodic variations adapted when burning to eject a predetermined number of molten droplets per unit length of the strand. According to one embodiment, each strand has a coiled configuration with a diameter of from 0.010 to 0.030 inch and a pitch of from 20 to 300 turns per inch. In an alternative embodiment, each strand is crimped to provide a plurality of substantially straight segments of approximately equal length interconnected at sharp bends in the strand. The length of each segment may be from 0.010 to 0.060 inch, and the bend angle may be from 60 to When ignited and burning in a flashlamp, combustible foil strands configurated according to the invention produce a greater number of molten droplets in flashlamps without altering the quantity of combustible material, fulminating material, or gas fill. In particular, the uniformity of the periodic variations in the strand configuration causes droplets of substantially uniform size to be ejected by centrifugal force when the strand is burning, and the dimensional constraints on the configuration provide for a significant reduction in size (and thus increase in number) of the ejected droplets.

Use of the combustible foil configurations of the invention, with the resulting increased number of smaller droplets during ignition, has been observed to provide from the fact that the smaller droplets increase the radiant surface area per milligram of shred burned. That is, the specific surface area per unit volume of the droplets is increased. More specifically, we feel that oxygen uptake by a droplet is primarily a surface reaction, which implies that the droplet surface area is important in determining the eventual light emitting capabilities of photoflash lamps. Assuming no increase in selfabsorbtion of emitted light from a greater number of droplets, the surface area of individual droplets should be directly proportional to lamp light output. In addition, we feel that the thinner oxide crust on the smaller droplet gives a higher droplet surface temperature and, thus, more efficient combustion and radiation in the visible end of the spectrum.

BRIEF DESCRIPTION OF THE DRAWINGS This invention will be more fully described hereinafter in conjunction with the accompanying drawings, in which:

FIG. 1 is an enlarged sectional elevation of an electrically ignitable photoflash lamp containing a filamentary combustible of coiled strand configuration in accordance with the invention;

FIG. 2 is an enlarged sectional elevation of a percussive-type photoflash lamp containing a filamentary combustible of crimped strand configuration in accordance with the invention;

FIG. 3 is a greatly enlarged view of a portion of one of the coiled strands of combustible foil employed in the lamp of FIG. 1;

FIG. 4 is an end view of the coiled strand of FIG. 3 wherein the coil configuration is circular;

FIG. 5 is an end view of the coiled strand of FIG. 3 wherein the coil configuration has been deformed to change the radius of curvature;

FIG. 6 shows comparative curves of relative light output vs. time for straight and coiled shreds;

FIG. 7 is a greatly enlarged view of a portion of one of the crimped strands of combustible foil employed in the lamp of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT The teachings of the present invention are applicable to either percussive or electrically ignited photoflash lamps of a wide variety of sizes and shapes. Accordingly, FIGS. 1 and 2 respectively illustrate electrically ignited and percussive-type photoflash lamps embodying the principles of the invention.

Referring to FIG. 1, the electrically ignitable lamp comprises an hermetically sealed lamp envelope 2 of glass tubing having a press 4 defining one end thereof and an exhaust tip 6 defining the other end thereof. Supported by the press 4 is an ignition means comprising a pair of lead-in wires 8 and 10 extending through and sealed into the press. A filament 12 spans the inner ends of the lead-in wires, and beads of primer l4 and 16 are located on the inner ends of the lead-in wires 8 and 10 respectively at their junction with the filament. Typically, the lamp envelope 2 has an internal diameter of less than one-halfinch, and in internal volume of less than 1 00., although the present invention is equally suitable for application to much larger lamp sizes. A combustion-supporting gas, such as oxygen, and a filamentary combustible material 18, such as shredded zirconium foil, are disposed within the lamp envelope. As

will be described in more detail hereinafter, the combustible 18 comprises a plurality of strands having a coiled configuration in accordance with the invention.

The percussive-photoflash lamp illustrated in FIG. 2 5 comprises a length of glass tubing defining an hermetically sealed lamp envelope 22 constricted at one end to define an exhaust tip 24 and shaped to define a seal 26 about a primer 28 at the other end thereof. The primer 28 comprises a metal tube 30, a wire anvil 32 and a charge of fulminating material 34. A combustible such as filamentary zirconium 36 and a combustionsupporting gas such as oxygen are disposed within the lamp envelope. As will be detailed hereinafter combustible 36 comprises a plurality of strands having a crimped configuration in accordance with the invention. The wire anvil 32 is centered within the tube 30 and is held in place by a circumferential indenture 38 of the tube 30 which laps over the head 40 or other suitable protuberance at the lower extremity of the wire anvil. Additional means, such as lobes 42 on wire anvil 32 for example, may also be used in stabilizing the wire anvil, supporting it substantially coaxial within the primer tube 30 and insuring clearance between the fulminating material 34 and the inside wall of the tube 30. A refractory bead 44 is fused to the wire anvil 32 just above the inner mouth of the primer tube 30 to eliminate burn-through and function as a deflector to deflect and control the ejection of hot particles of fulminating material from the primer. The lamp of FIG. 2 is also typically a subminiature type having dimensions similar to those described with respect to FIG. 1.

Although the lamp of FIG. 1 is electrically ignited, usually from a battery source, and the lamp of FIG. 2 is percussion-ignitable, the lamps are similar in that in each the ignition means is attached to one end of the lamp envelope and disposed in operative relationship with respect to the filamentary combustible material. More specifically the igniter filament 12 of the flash lamp in FIG. 1 is incandesced electrically by current passing through the metal filament support leads 8 and 10, whereupon the incandesced filament ignites the beads of primer l4 and 16 which in turn ignite the combustible 18 disposed within the lamp envelope. Operation of the percussive-type lamp of FIG. 2 is initiated by an impact onto tube 30 to cause deflagration of the fulminating material 34 up through the tube 30 to ignite the combustible 36 disposed within the lamp envelope. The invention is also applicable to other types of electrically ignited lamps, such as those having spark gap or primer bridge ignition structures.

As previously mentioned, the filamentary combustible employed in flash lamp envelopes normally comprises a shredded metallic foil, such as zirconium. The metallic foil manufactured for this application is nor mally provided in thicknesses of about or somewhat less than 1 mil and in widths of about 4 inches. The foil is then processed through standard shredding equipment to produce desirable cross sections of about 1.0 to 2.0 square mils, depending upon the characteristics of various photoflash lamps. Accordingly, the strands of shredded foil in photoflash lamps are normally about 4 inches long, although there are many applications in which the foil is split to provide much shorter strand lengths for the filamentary combustible.

In accordance with the present invention, we have discovered that by winding shreds of zirconium, or other droplet forming combustibles, on a mandrel ranging in diameter from 0.010 inch to 0.030 inch with varying turns per inch, a strand configuration is provided, as shown in FIG. 3, which promotes the formation of a varying quantity of molten droplets from the coil windings during combustion. This invention does not necessitate the specific use of narrow shreds of combustible material cut from a broad ribbon of foil but may also employ wire filaments of combustible. As a typical example, we have found that a 40 turns per inch winding of a 1.2 inch length of zirconium strand, having a cross-section of about 0.85 X 1.2 mils (about 0.18 mg./in), about the circumference of a 0.010 inch tungsten mandrel yeilded to droplets upon combustion, compared to 1 to 2 droplets from an equivalent length of straight shred material. In our example we found that removing all twists from the shreds prior to the winding operation greatly facilitates coil removal from the mandrel. We also chose to wind coils tightlyone turn abutting the next-so that any desired coil pitch could be obtained by subsequent coil elongation. Obviously, the proper coil pitch could be obtained during the winding operation. The use of a mandrel was found helpful in obtaining our combustible coils although it is not essential.

We have found that depending on the cross-sectional area of the strands and mandrel sizes and number of turns per inch of the coil winding, the number of droplets ejected from a burning strand can be varied over quite a range. Referring to FIG. 3, we feel that the centrifugal force acting on the main droplet 46 travelling along the turns of the coil 48 is responsible for the periodic ejection of smaller secondary droplets. We have observed that when a droplet is flung from the coil due to centrifugal action, another droplet is left remaining which then proceeds along the coil until it is eventually ejected. This process repeats itself until all shred material is consumed. It would appear from our observations that the centrifugal force acting upon the droplet proceeding down the coil is sufficient to overcome the surface tension forces holding the drop on the burning wire, thereby causing periodic formation of small secondary drops. Based on these observations, coil pitch and diameter and the mass of the droplet would be the determining factors in secondary droplet formations. That is, centrifugal force mv /r. The velocity (v) is generally constant. The radius of curvature (r) is dependent on the mandrel size, i.e., the diameter of a circular coil (FIG. 4), and the coil pitch, or turns per inch. The mass (m) of the droplet is proportional to the weight per unit length of burned coil, which in turn is dependent on the cross-sectional area of a selected combustible material. In accordance with the present invention, therefore, the filamentary combustible material 18 filling the lamp of FIG. 1 comprises a plurality of strands each having a coiled configuration (FIG. 3) wherein the cross-sectional area of the strands and the pitch and diameter of the coiled configuration are selected to produce a predetermined number of molten droplets per unit of strand length upon ignition. In practice, the desired coil parameters are determined experimentally. We have found, for example, that high speed photography of coiled shreads with varying parameters can be useful in determining desired characteristics. It may generally be noted, from the above centrifugal force relationship, that the droplets ejected from a coil may be increased by an increase in the turns per inch, a reduction of the radius of curvature, or an increase in the strand cross-section.

As previously discussed, the shredded foil presently employed in flashlamps ranges from 1 to 2 square mils in cross-sectional area.

Typical coil pitch values found to give desired results ranged from 20 to 300 turns per inch. A limiting factor would arise when coil turns abutted one another so as to cause the droplet to bridge individual turns, rather than travel around the individual coil turns. At the other extreme, the limiting factor would be when coil turns are extended to such a degree that essentially a straight shred is obtained.

Mandrel diameters could range from a minimum where initial droplet size does not exceed coil internal diameter, or at the other extreme where the mandrel diameter does not exceed the diameter or the combustion vessel. As described above, we have obtained desired results with coil diameters ranging from 0.010 to 0.030 inch, which represents a range of from about 0.031 to 0.094 inch for the length of strand comprising each periodic variation, or loop, of the configuration.

Strand length may vary from the minimum necessary to provide self-support of the filamentary combustible in a given lamp envelope size to the maximum available from currently employed shredding equipment. More specifically, the length of the coiled configuration of the strand should not be much less than the inside diameter of the lamp envelope, and before being coiled, the strand may be up to 8 inches long, unless limited by a very small lamp volume.

We have indicated that use of the above coil configuration provides an increased number of smaller droplets and thereby increases the specific area of the ignited combustible material, which in turn results in a higher light output. Actual comparative measurements conducted on individual straight shreds versus equivalent weights of coiled shred material (0.010 inch diameter, turns per inch) have resulted in the following relative light output values obtained every 1.25 msec. during the combustion process.

Relative Light Output Gain Time Straight Shred Coiled Shred or Loss ITISCC 1.25 365 703 +926 2.50 844 1446 +71.3 3.75 1317 1689 +282 5.00 1655 2569 +552 6.25 2052 2746 +340 7.50 2338 2848 +21.8 8.75 2443 3173 +29.9 10.0 2755 4331 +572 11.25 3589 5633 +569 12.50 3839 5682 +480 13.75 3719 4982 +33.9 15.0 3560 4003 +124 16.25 3395 3136 -7.7 17.50 3210 2548 -l9.7 18.75 3106 2242 27.8 20.0 3045 2120 30.4 30.0 1882 628 66.3

These data substantiate that the coiled shred embodiment indeed produces substantial improvements in initial light output and peak light output. Lower relative light output values beyond '16 msec should not greatly affect performance of these coiled shreds in lamps since little light is desired after this time interval.

The comparative light output characteristics of boiled vs. straight shreds are also illustrated by the curves of FIG. 6. The same quantity of combustible was burned in both cases; namely, 0.6 inch lengths of zirconium shreds having equal cross-sections were burned at a constant oxygen pressure. The coiled shred was wound on a 0.010 inch mandrel with 80 turns per inch. It will be noted that the light energy produced by the burning coiled shred is compressed toward the peak time, with the coiled shred exhibiting a peak light output which is well over 20 percent higher than the peak output of the straight shred.

As a variation of the circular coil embodiment of FIG. 4, we have found that the application ofa uniform load bearing force across the turns of the fabricated combustible coils can be advantageous in terms of increasing the number of droplets formed. The effect of deformation would be to increase the radius of curvature. the droplet 46 must follow in the path along the deformed coil 49, as illustrated in FIG. 5.

An alternative embodiment of the invention is to provide a uniformly crimped, or zig-zag, strand configuration, as illustrated in FIG. 7. One method of obtaining this configuration is to apply sufficient load bearing forces to completely flatten a coiled strand. An alternative method of providing crimped strands is to pass straight strands through a pair of intermeshing gears or knurled wheels.

When a crimped strand is ignited, a molten droplet 50 is forced to travel in a single plane, much like the traveling of an object along a sinusoidal wave. Preferably, the crimped configuration of FIG. 7 comprises a plurality of substantially straight segments 52 of approximately equal length interconnected at sharp bends 54 in the strand. Here again, we feel that centrifugal force may be viewed as instrumental in the droplet ejection process and we have determined that the principal factors affecting droplet formation include the cross-sectional area of the strand, the bend angle (FIG. 7), and the length of segments 52. Identical factors would be derived by considering that droplet formation occurs when inertia of the moving droplet exceeds the restraining forces resulting from surface tension. In accordance with the present invention, therefore, the filamentary combustible material 36 filling the lamp of FIG. 2 comprises a plurality of strands each having a crimped configuration (FIG. 7) wherein the cross-sectional area of the strands, the length of the segments 52, and the angle 6 of the bends 54 are selected to produce a predetermined number of molten droplets per unit of strand length upon ignition. As a typical example, we have observed from high speed photographs a yield of 20 to 30 droplets from a 1.2 inch strand of crimped zirconium foil having a cross-section of about 0.85 X 1.2 mils (about 0.1 8 mg./in.), with each of the segments 52 having a length of approximately 0.022 inch, and each of the bend angles 0 being approximately 135.

As previously discussed, the shredded foil presently employed in flashlamps ranges from I to 2 square mils in cross-sectional area. As the cross-section increases, the frequency of droplet formation increases, and individual droplets will be larger.

Segment lengths also effect the size and periodicity of droplet formation-longer segments produce larger and fewer droplets, but segments that are too short result in crimp bridging, which also causes fewer droplets to be produced. We have determined that segment 52 lengths in the order of about 0.010 inch to about 0.060 inch will tend to maximize the number of droplets formed, assuming bend angles 0 of 135 and a weight of combustible per unit length in the order of 0.18 mg./in. This represents a range of from about 0.020 to 0.120 inch for the length of strand comprising each periodic variation, or zig-zag, of the configuration. Since a principal object of the invention is to produce the maximum number of droplets per unit length of combustible material, it is advantageous to maintain the segment lengths within the above limits.

Bend angles have been found to have an influence on the frequency of droplet formation. We have determined, for example, that bend angles 0 (see FIG. 7) less than about 60 are not as effective in producing the desired multiplicity of droplets. This decrease in number of droplets encountered with small bend angles is undoubtedly due to the decrease in centrifugal force acting on the droplet. We have also determined that bend angles greater than about are not preferable because of the possibility of droplet bridging between adjacent shred segments.

In addition to the advantages of increased droplet formation and the forming of uniformly smaller droplets, the use of coiled or crimped strands of combustible has a distinct advantage over previous embodiments in terms of the quantity of point contacts made with the wall surfaces of the lamp envelope. We have determined, for example, that coils wound on a 0.010 inch mandrel having 40 turns per inch form essentially point contacts every 0.020 inch along the envelope walls, thus eliminating practically all lateral contacts and thereby substantially reducing the undesired quenching effect of the glass envelope. This point contact relationship is illustrated between the coiled combustible l8 and lamp envelope 2 in FIG. 1 and between the crimped combustible 36 and lamp envelope 22 in FIG. 2.

Another distinct advantage of these periodically varying shred configurations, which is particularly noticeable in the coiled strands, is that lateral contacts between individual strands in the lamp envelope are minimized due to the many point contacts generated by the coiled and crimped windings. In this connection, the coiled and crimped configurations tend to prevent roping of the strand, thereby reducing opportunities for the droplets to coalesce and produce undesired larger droplets.

A further advantage of the coiled and crimped shreds in larger volume flashlamps is that a larger number of smaller droplets are obtained without having to contend with the problems of crumpled and short shreds falling to the envelope walls due to vibrational effects. That is, the coiled and crimped shreds have a built-in means for periodic droplet ejection regardless of length, whereas crumpled and short shred configurations are each dependent on length plus cross-sectional area.

Yet another advantage of the coiled and crimped shred configurations in lamps, as evidenced by high speed photography, is that droplets striking a coiled or crimped structure can cause the formation of a plurality of small droplets because of the many coil turns or crimps simultaneously ignited.

Although the invention has been described with respect to specific embodiments, it will be appreciated that modifications and changes may be made by those skilled in the art without departing from the true spirit and scope of the invention. Although the lamps of FIGS. 1 and 2 are illustrated as containing coiled and crimped combustible strands, respectively, it should be clear that crimped strands may also be used in electrically ignitable lamps, and that coiled strands can be used in percussive-type lamps. Combustible materials other than zirconium may be used. For purposes of the droplet formation advantages of the invention, it is clear that the filamentary material should comprise a combustible which burns at the surface of a molten globule by oxygen diffusion through an oxide coating thereon, such as zirconium, hafnium, thorium, or combinations thereof, rather than a combustible which burns as a vapor, such as aluminum or magnesium. Nevertheless, the coiled configuration can also prove useful for filamentary combustibles of aluminum or magnesium, as the anti-roping and point contact features are conducive to improved light output from these materials also.

What we claim is:

l. A photoflash lamp comprising:

an hermetically sealed, light-transmitting envelope;

a combustion-supporting gas in said envelope;

a quantity of filamentary combustible material located within said envelope, said filamentary material comprising a plurality of strands each having a configuration of substantially uniform periodic variations adapted when burning to eject therefrom a predetermined number of molten droplets per unit length of said strand, the length of strand comprising each of said periodic variations being from about 0.020 to 0.120 inch;

and ignition means attached to one end of said envelope and disposed in operative relationship with respect to said combustible material.

2. A lamp according to claim 1 wherein said filamentary material comprises a combustible which when ignited burns at the surface of a molten globule by oxygen diffusion through an oxide coating thereon.

3. A lamp according to claim 2 wherein the material comprising said filamentary combustible is selected from the group consisting of zirconium, hafnium, thorium, and combinations thereof.

4. A lamp according to claim 1 wherein the peroidically varying configuration of each of said strands is formed to cause molten droplets of substantially uniform size to be ejected by centrifugal force when the strand is burning.

5. A lamp according to claim 1 wherein each of said strand of filamentary material has a coiled configuration.

6. A lamp according to claim 1 wherein each of said strands of filamentary material has a crimped configuration comprising a plurality of substantially straight segments of approximately equal length interconnected at sharp bends in the strand.

7. A lamp according to claim 6 wherein the crosssectional area of each of said strands, the length of said segments, and the angle of said bends are selected to produce a predetermined number of molten droplets per unitof strand length upon ignition.

8. A lamp according to claim 6 wherein each of the substantially straight segments of said strands of filamentary material has a length of about 0.010 to 0.060 inch.

9. A lamp according to claim 6 wherein the angle of each of the sharp bends in said strand of filamentary material is not less than about 60 and not more than about 10. A lamp according to claim 6 wherein said crimped configuration has a segment length of about 0.010 to 0.060 inch and a bend angle of not less than aobut 60 and not more than about 165.

11. A lamp according to claim 6 wherein said filamentary material comprises crimped strands of shredded zirconium foil.

12. A lamp according to claim 11 wherein each of said crimped strands has a segment length of about 0.010 to 0.060 inch and a bend angle of not less than about 60 and not more than about 165.

13. A lamp according to claim 12 wherein each of said strands of zirconium foil has a cross-sectional area of about 1 to 2 square mils.

14. A lamp according to claim 13 wherein the crimped configuration of said strands has a length approximately equal to or greater than the inside diameter of said envelope.

15. A photoflash lamp comprising:

a hermetically sealed, light-transmitting envelope;

a combustion-supporting gas in said envelope;

a quantity of filamentary combustible material located within said envelope, said filamentary material comprising a plurality of strands each having a uniform coiled configuration having a diameter of from about 0.010 to 0.030 inch and a pitch of from about 20 to 300 turns per inch;

and ignition means attached to one end of said envelope and disposed in operative relationship with respect to said combustible material.

16. A lamp according to claim 15 wherein the crosssectional area of each of said strands and the pitch and diameter of said coiled configuration are selected to produce a predetermined number of molten droplets per unit of strand length upon ignition.

17. A lamp according to claim 15 wherein the diameter of said coiled configuration is larger than that of the molten droplets produced upon ignition of said strands and smaller than the diameter of said envelope.

18. A lamp according to claim 15 wherein said filamentary material comprises coiled strands of shredded zirconium foil.

19. A lamp according to claim 18 wherein each of said strands of zirconium foil has a cross-sectional area of about 1 to 2 square mils.

20. A lamp according to claim 19 wherein the coiled configuration of said strands has a length approximately equal to or greater than the inside diameter of said envelope. 

1. A photoflash lamp comprising: an hermetically sealed, light-transmitting envelope; a combustion-supporting gas in said envelope; a quantity of filamentary combustible material located within said envelope, said filamentary material comprising a plurality of strands each having a configuration of substantially uniform periodic variations adapted when burning to eject therefrom a predetermined number of molten droplets per unit length of said strand, the length of strand comprising each of said periodic variations being from about 0.020 to 0.120 inch; and ignition means attached to one end of said envelope and disposed in operative relationship with respect to said combustible material.
 2. A lamp according to claim 1 wherein said filamentary material comprises a combustible which when ignited burns at the surface of a molten globule by oxygen diffusion through an oxide coating thereon.
 3. A lamp according to claim 2 wherein the material comprising said filamentary combustible is selected from the group consisting of zirconium, hafnium, thorium, and combinations thereof.
 4. A lamp according to claim 1 wherein the peroidically varying configuration of each of said strands is formed to cause molten droplets of substantially uniform size to be ejected by centrifugal force when the strand is burning.
 5. A lamp according to claim 1 wherein each of said strand of filamentary material has a coiled configuration.
 6. A lamp according to claim 1 wherein each of said strands of filamentary material has a crimped configuration comprising a plurality of substantially straight segments of approximately equal length interconnected at sharp bends in the strand.
 7. A lamp according to claim 6 wherein the cross-sectional area of each of said strands, the length of said segments, and the angle of said bends are selected to produce a predetermined number of molten droplets per unit of strand length upon ignition.
 8. A lamp according to claim 6 wherein each of the substantially straight segments of said strands of filamentary material has a length of about 0.010 to 0.060 inch.
 9. A lamp according to claim 6 wherein the angle of each of the sharp bends in said strand of filamentary material is not less than about 60* and not more than about 165*.
 10. A lamp according to claim 6 wherein said crimped configuration has a segment length of about 0.010 to 0.060 inch and a bend angle of not less than aobut 60* and not more than about 165*.
 11. A lamp according to claim 6 wherein said filamentary material comprises crimped strands of shredded zirconium foil.
 12. A lamp according to claim 11 wherein each of said crimped strands has a segment length of about 0.010 to 0.060 inch and a bend angle of not less than about 60* and not more than about 165*.
 13. A lamp according to claim 12 wherein each of said strands of zirconium foil has a cross-sectional area of about 1 to 2 square mils.
 14. A lamp according to claim 13 wherein the crimped configuration of said strands has a length approximately equal to or greater than the inside diameter of said envelope.
 15. A photoflash lamp comprising: an hermetically sealed, light-transmitting envelope; a combustion-supporting gas in said envelope; a quantity of filamentary combustible material located within said envelope, said filamentary material comprising a plurality of strands each having a uniform coiled configuration having a diameter of from about 0.010 to 0.030 inch and a pitch of from about 20 to 300 turns per inch; and ignition means attached to one end of said envelope and disposed in operative relationship with respect to said combustible material.
 16. A lamp according to claim 15 wherein the cross-sectional area of each of said strands and the pitch and diameter of said coiled configuration are selected to produce a predetermined number of molten droplets per unit of strand length upon ignition.
 17. A lamp according to claim 15 wherein the diameter of said coiled configuration is larger than that of the molten droplets produced upon ignition of said strands and smaller than the diameter of said envelope.
 18. A lamp according to claim 15 wherein said filamentary material comprises coiled strands of shredded zirconium foil.
 19. A lamp according to claim 18 wherein each of said strands of zirconium foil has a cross-sectional area of about 1 to 2 square mils.
 20. A lamp according to claim 19 wherein the coiled configuration of said strands has a length approximately equal to or greater than the inside diameter of said envelope. 